ABSTRACT This proposal will determine the relationships between lung injury and mortality in sepsis and plasmalogen- derived chlorinated lipids, which are produced during the innate immune response. A significant cause of morbidity and mortality in patients worldwide, sepsis is the systemic dysregulation of the immune response to an initial infection and often leads to acute lung injury (ALI), other organ damage, and death. Host neutrophils are a component of the innate immune system and are systemically activated during sepsis. Neutrophil myeloperoxidase (MPO) is important in bacterial killing during sepsis. MPO catalyzes the production of hypochlorous acid (HOCl) from hydrogen peroxide produced during the respiratory burst. HOCl, in turn, is a powerful oxidant that targets microbes. However, HOCl may also react with host molecules, including the vinyl ether bond of membrane plasmalogens. Plasmalogens are a class of glycerophospholipids with an aliphatic chain connected to the glycerol backbone through a vinyl ether bond. When attacked by HOCl, the aliphatic chain is liberated as chlorofatty aldehyde (2-ClFALD). 2-ClFALD can be oxidized to chlorofatty acid (2-ClFA) under physiologic conditions. These compounds, designated as plasmalogen-derived chlorinated lipids, are elevated in a variety of inflammatory conditions. A Ford lab manuscript in review demonstrates plasma 2-ClFA predicts acute respiratory distress syndrome-associated mortality in sepsis. Other projects suggest plasmalogen-derived chlorinated lipids elicit endothelial dysfunction, a major causative factor of ALI. We hypothesize that plasmalogen-derived chlorinated lipids are critical mediators of acute lung injury and mortality in sepsis through their role in eliciting endothelial dysfunction. Aim 1 of this proposal will use a cecal slurry (CS) model of sepsis in rats to determine if plasmalogen-derived chlorinated lipid production predicts sepsis outcomes, such as mortality, endothelial dysfunction, and lung injury. Mechanistic studies will be employed to demonstrate causative roles of MPO and 2-ClFA in CS elicited mortality, endothelial dysfunction, and lung injury. Aim 2 will determine that plasmalogen-derived chlorinated lipids cause endothelial dysfunction and lung injury in the absence of sepsis by giving rats exogenous 2-ClFA. A click chemistry analog of 2-ClFA will visualize the localization of the lipid to lung endothelium. Additional experiments will examine 2-ClFA-elicited gut permeability. The mechanisms through which 2-ClFA elicits endothelial dysfunction will also be explored using human lung endothelial cells. Current treatment regimens for sepsis and sepsis-related ALI consist of antibiotics and supportive care, with a noticeable paucity in treatments targeting the dysregulated host response. Further understanding of the mechanisms mediating lung damage and pathology in sepsis is vital for the development of more efficacious treatments and diagnostic strategies. A comprehensive training plan is proposed that includes these exciting studies to develop needed skills for my career goal to become a clinician-scientist.